Theoretical approach to resonant inelastic x-ray scattering in iron-based superconductors at the energy scale of the superconducting gap

摘要

We develop a phenomenological theory to predict the characteristic featuresof the momentum-dependent scattering amplitude in resonant inelastic x-rayscattering (RIXS) at the energy scale of the superconducting gap in iron-basedsuperconductors. Taking into account all relevant orbital states as well astheir specific content along the Fermi surface we evaluate the charge and spindynamical structure factors for the compounds LaOFeAs and LiFeAs, based ontight-binding models which are fully consistent with recent angle-resolvedphotoemission spectroscopy (ARPES) data. We find a characteristic intensityredistribution between charge and spin dynamical structure factors whichdiscriminates between sign-reversing and sign-preserving quasiparticleexcitations. Consequently, our results show that RIXS spectra can distinguishbetween $s_\pm$ and $s_{++}$ wave gap functions in the singlet pairing case. Inaddition, we find that an analogous intensity redistribution at small momentacan reveal the presence of a chiral $p$-wave triplet pairing.